1. Field of the Invention
The present invention relates to compression-release engine brake systems in general, and more particularly to a compression-release engine brake system and method comprising a lost motion type engine brake rocker arm assembly incorporating structure implementing a valve reset function.
2. Description of the Related Art
Compression release engine brake systems (or retarders) for diesel engines were designed and developed in North America starting in the early 1960's. There have been many changes that have been implemented that have increased retarding performance, reduced cost, reduced engine loading and reduced engine valve train loading.
Conventionally, the engine brake compression release retarders change a power producing diesel engine to a power absorbing air compressor. The air in the cylinder is compressed on the compression stroke and is released near top dead center (TDC) of the compression stroke just prior to the expansion stroke to reduce the cylinder pressure and prevent it from pushing the piston down on the expansion stroke. In the so-called exhaust brake systems, work on the air is done on the exhaust stroke when the piston is moving up and there may be a pressure increase in the exhaust manifold from turbocharger restriction or other exhaust restriction.
The opening of the exhaust valve(s) near TDC to vacate cylinder pressure can be accomplished by a number of different approaches. Some of the most common methods used are add-on housings that hydraulically transfer intake or exhaust cam motion from a neighboring cylinder, or fuel injector motion from the same cylinder to provide a method of timing the exhaust valve(s) to open near TDC of the compression stroke to optimize the release of compressed air in the cylinder.
Other engine brake systems have a rocker arm brake that utilizes an exhaust rocker arm (or lever) to open the exhaust valve(s) near TDC of the compression stroke. A term used to identify a type of rocker arm brake is a lost motion concept. This concept adds an additional small lift profile to the exhaust cam lobe that opens the exhaust valve(s) near TDC of the compression stroke when excess exhaust valve lash is removed from the valve train.
Rocker arm brake systems using the lost motion principle have been known for many years. One problem with the conventional rocker arm brake system is that valve overlap at exhaust/intake is extended and thus braking performance decreased. Moreover, a problem with opening a single valve is that exhaust/intake overlap is extended and valve opening by an exhaust bridge may be unbalanced during the initial normal exhaust lift and may result in engine overhead damage. Extended overlap allows exhaust gas to flow backwards into the engine from the exhaust manifold and through the inlet valve into the inlet manifold. In other words, the extended valve overlap causes an undesired exhaust manifold air mass flow into the engine intake system, thus reducing exhaust stroke work and decreasing braking performance.
Embodiments disclosed herein can operate to open an exhaust valve late in the expansion stroke, to open an exhaust valve at a faster rate, and to evacuate the cylinder quickly to provide a very high performance engine brake.